Power tool, system, and method

ABSTRACT

A power tool with a rotatable tool designed as a saw blade or a milling cutter, including a sensor device for detecting a mechanical quantity, the mechanical quantity having a force, an acceleration, a velocity, a deflection, a deformation and/or a mechanical stress, and the mechanical quantity being dependent on a force emanating from the tool, and a control device communicatively coupled to the sensor device, which control device is adapted to recognize a kickback event based on the detected mechanical quantity, where the control device is adapted to selectively determine a first recognition function or a second recognition function different from the first recognition function based on a function determination information, and to perform the recognition of the kickback event based on the detected mechanical quantity using the determined recognition function.

This application is a Divisional of U.S. patent application Ser. No.16/632,991 filed Jan. 22, 2020, which is a US National Stage applicationbased on PCT/EP2017/068648 filed on Jul. 24, 2017, which applicationsare incorporated herein by reference

The invention relates to a power tool with a rotatable tool designed asa saw blade or a milling cutter, a sensor device for detecting amechanical quantity, the mechanical quantity comprising a force, anacceleration, a velocity, a deflection, a deformation and/or amechanical stress and the mechanical quantity depending on a forceemanating from the saw blade, and a control device communicativelycoupled to the sensor device, which control device is adapted torecognize a kickback event of the power tool based on the detectedmechanical quantity.

BACKGROUND OF THE INVENTION

The term “kickback event” refers in particular to an event in which,during machining of a workpiece by the power tool, a sudden andunexpected force occurs between the power tool and the workpiece, whichthen accelerates and sets the power tool or the workpiece in motion.With circular table saws, a kickback usually leads to an unexpectedacceleration of the workpiece in the direction of the user. Withcircular hand saws, a kickback can cause unexpected movements of thetool. Kickbacks can lead to injuries to the user and therefore representan impairment of the operational safety. A kickback event can occur inparticular if the tool is plunged jerkily and too quickly into theworkpiece, if the tool is sawing backwards, if the tool is jammed in theworkpiece, if specific workpiece properties (e.g. inhomogeneous wood,stresses) are present and/or if the tool is blunt.

WO 2014/105935 A1 describes a table saw with a kickback detection systemcomprising a sensor adapted to detect a deflection of a shaft as ascalar quantity. A controller compares the detected deflection with ascalar threshold value to determine whether a kickback is present.

SUMMARY OF THE INVENTION

It is an object of the invention to modify the aforementioned power toolin such a way that the usability of the power tool is improved.

The object is solved by a power tool according to claim 1. In accordancewith the invention, the control device is adapted to selectivelydetermine, based on a function determination information, a firstrecognition function or a second recognition function different from thefirst recognition function and to perform the recognition of thekickback event based on the detected mechanical quantity using thedetermined recognition function.

The control device is therefore able to determine one of at least twodifferent recognition functions for recognizing the kickback event. Thecontrol device therefore has various recognition functions available foruse. The control device determines one of these recognition functionsand uses the determined recognition function to perform the recognitionof the kickback event.

Since the control device has various recognition functions available touse and one of the recognition functions is determined based on thefunction determination information, it becomes possible to use, withrespect to a current operating state and/or environmental state, theoptimum recognition function. For example, the function determinationinformation (and thus the recognition function to be used) can beprovided based on which user is using the power tool, what tool is beingused and/or what workpiece is to be machined.

For example, if the current user is a particularly inexperienced user, aparticularly sensitive recognition function can be determined to ensurethat weak kickbacks are also recognized by the control device. For aparticularly experienced user, on the other hand, it is advisable todetermine a particularly insensitive recognition function so that onlyparticularly strong kickbacks are recognized and unnecessaryinterruption of the machining is avoided.

Thus, by the selective determination of a recognition function from atleast two different recognition functions, the usability of the powertool can be improved.

Expediently, the control device is adapted to use only one recognitionfunction, namely the previously determined recognition function, todetect the kickback event. This means that the control device ispreferably adapted to use either the first or the second recognitionfunction to detect the kickback event.

Advantageous embodiments are defined in the dependent claims.

The invention further relates to a system comprising the power tooldiscussed above and an external device, in particular a server. Thepower tool is adapted to transmit operating information and/orenvironmental information and/or user identification information to theexternal device. The external device is adapted to provide functiondetermination information based on the operating information and/orenvironment information and/or user identification information and totransmit the function determination information to the power tool.

The invention further relates to a method for recognizing a kickbackevent of a power tool with a rotatable tool in the form of a saw bladeor a milling cutter. The method comprises the steps of: detecting amechanical quantity, wherein the mechanical quantity comprises a force,an acceleration, a velocity, a deflection, a deformation and/or amechanical stress, and the mechanical quantity depends on a forceemanating from the tool; determining, based on a function determinationinformation, a recognition function to be used from a first recognitionfunction and a second recognition function different from the firstrecognition function; and recognizing, using the determined recognitionfunction, the kickback event based on the detected mechanical quantity.

Expediently, the method is performed with a power tool described here.

BRIEF DESCRIPTION OF THE DRAWINGS

Further exemplary details as well as exemplary embodiments are explainedbelow with reference to the drawing. Thereby shows

FIG. 1 a schematic illustration of a power tool,

FIG. 2 a diagram illustrating a kickback detection based on a directionof a mechanical vector quantity,

FIG. 3 a sectional view of a power tool,

FIG. 4 a sectional view of an output shaft and two bearings of the powertool,

FIG. 5 a schematic illustration of a power tool, and

FIG. 6 a block diagram of a method.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a power tool 10 according to a first embodiment.

The power tool 10 has a rotatable tool 1, which is exemplarily designedas a saw blade. Alternatively, the tool 1 can also be designed as amilling cutter. The power tool 10 comprises a sensor device 2 fordetecting a mechanical quantity 3. The mechanical quantity 3 comprises aforce, an acceleration, a velocity, a deflection, a deformation and/or amechanical stress. The mechanical quantity 3 depends on a forceemanating from the tool 1. The power tool further has a control device 4which is communicatively coupled to the sensor unit 2. The controldevice 4 is adapted to recognize a kickback event based on the detectedmechanical quantity 3.

The control device 4 is adapted to determine, based on a functiondetermination information, selectively a first recognition function or asecond recognition function different from the first recognitionfunction. The control device 4 is further adapted to perform thekickback event recognition based on the detected mechanical quantityusing the determined recognition function.

Since the control device 4 can determine a recognition function fromseveral available recognition functions and can use it to recognize thekickback event, it becomes possible to use a recognition function thatis most suitable for a current state and to thus improve the usabilityof the power tool 10.

In the following, exemplary details of the power tool 10 as well asother exemplary embodiments are explained.

The power tool 10 is preferably a saw, in particular a hand-heldcircular saw or a plunge saw. The power tool 10 can also be designed asa flat dowel milling machine. The tool 1 is in particular circular androtates clockwise in operation, for example.

Exemplarily, the power tool 10 has a housing 6, in which in particularthe sensor device 2 and the control device 4 are arranged. The controldevice 4 is designed as a microcontroller, for example. A contactsurface 9 is provided on the housing 6, with which contact surface thepower tool 10 can be placed on a workpiece 11 to be machined.

The power tool 10 has a drive device 7, which includes, for example, anelectric motor and a gearbox. The drive device 7 is preferablycontrolled by the control device 4. The power tool 10 further has anoutput shaft 8, which can be driven by the drive device 7. The tool 1 ismechanically coupled to the output shaft 8. Expediently, the tool 1 isattached to the output shaft 8.

As shown in FIG. 1, when machining the workpiece 11, the power tool 10typically lies on the workpiece 11 with the contact surface 9 and ismoved in a feed direction 12 relative to workpiece 11. Exemplarily, thesaw teeth of the tool 1, which is designed as a saw blade, saw into theworkpiece 11 from bottom to top. In this constellation, the tool 1 urgesrelative to the rest of the power tool 10 in the direction of themechanical quantity 3, i.e. diagonally downwards. The force emanatingfrom the saw blade 1 points in particular in the direction of themechanical quantity 3.

The power tool 10 further has a support structure 21, which isexpediently located in the housing 6. The output shaft 8, for example,is mounted on the support structure 21. Furthermore, the supportstructure 21 can be designed as a housing for the drive device 7. Thesupport structure 21 may, for example, represent or comprise a drivehousing, in particular a gearbox housing.

Exemplarily, the power tool 10 also has a user input device 5. Via theuser input device, the user can make a user input, for example forswitching the power tool 10 on and off and/or for configuring and/orcalibrating the power tool 10.

Furthermore, the power tool 10 exemplarily has a communication interface35. The communication interface 35 serves for communication with anexternal device 38, in particular an external server and/or a mobiledevice. The communication interface 35 is in particular adapted forwireless and/or wired communication. For example, the communicationinterface 35 is adapted to communicate via Ethernet, WLAN, Bluetoothand/or NFC.

The power tool 10 exemplarily further comprises a user identificationdevice 36. The user identification device 36 is adapted to detect a useridentification information, preferably a property, in particular abiometric property, of a user in order to enable an identification ofthe user, for example by the control device 4. For example, the useridentification device 36 has a fingerprint scanner and/or an imagesensor.

Exemplarily, the sensor device 2 has two sensor units 33, 34. Thealready mentioned detection of the mechanical quantity 3 is exemplarilycarried out by the first sensor unit 33. In FIG. 1, the sensor device 2or the first sensor unit 33 is exemplarily coupled to the output shaft 8and is adapted to detect the mechanical quantity 3—namely a force,acceleration, velocity, deflection, deformation and/or mechanicalstress—of the output shaft 8. Expediently, the mechanical quantity 3 isa vector quantity. Preferably, the sensor device 2 is adapted tocontinuously detect the mechanical quantity 3, so that a change,especially a change in direction of the mechanical quantity 3 can bedetected.

The sensor device 2 is preferably further adapted to detect operatinginformation and/or environmental information. For this purpose, thesensor device 2 in FIG. 1 optionally has the second sensor unit 34.Alternatively or additionally, it is also possible to use the firstsensor unit 33 to acquire operational and/or environmental information.

The operational and/or environmental information is, for example, aproperty of the tool 1, for example the type and/or a wear state of thetool 1.

For example, the sensor device 2 may include, as the second sensor unit34, an image sensor capable of taking an image of the tool 1, inparticular of a marking applied to the tool 1, such as a typedesignation. Based on the captured image, the control device 4 can thendetermine the type of the tool 1.

For determining a wear state of the tool 1, the control device 4 can,for example, be adapted to detect the mechanical quantity 3 as amechanical vector quantity and to infer the wear state if a specificdirection and/or change of direction of the mechanical vector quantityis given. As an alternative or in addition to this, the control device 4can be adapted to repeatedly detect the mechanical quantity 3 over alonger period of time or a plurality of uses of the power tool 10 and tocarry out a statistical evaluation of the detections, from which it isthen possible to draw conclusions about the wear state, for example onthe basis of a trend or a development or a deviation of an averagevalue.

In addition, as operating information and/or environmental information,a property of the workpiece 11 to be machined with the tool 1 can bedetected. For example, an image of the workpiece 11, in particular amarking 37 applied to workpiece 11, for example a type designation, canbe taken. Based on the captured image, the control device 4 can thendetermine the type of the workpiece 11.

Furthermore, the detected operational and/or environmental informationmay include a temperature and/or humidity. For example, the sensordevice 2 may, as the second sensor unit 34, include a temperature sensorand/or a humidity sensor.

In the example shown, the second sensor unit 34 and the useridentification device 36 are two different units.

Alternatively, especially when both the sensor unit 34 and the useridentification device 36 are used to take an image, the sensor unit 34and the user identification device 36 may be the same unit.

The two recognition functions and in particular the difference betweenthe recognition functions are explained in detail below.

In the simplest case, the recognition functions can each be a comparisonof the mechanical quantity 3 with a respective threshold, the comparisonbeing carried out by control device 4. For example, the mechanicalquantity 3 is detected as a scalar and is compared with a respectivescalar threshold. Alternatively or in addition to this, the mechanicalquantity 3 can also be detected as a vector quantity and the magnitudeof the vector quantity can be compared with a respective threshold. Ifthe threshold is exceeded, the control device 4 infers a kickback event.

Expediently, each recognition function is associated with a differentthreshold. For example, the threshold of the first recognition functionis greater than the threshold of the second recognition function.

Preferably, the second recognition function is more sensitive than thefirst recognition function. This means that when using the secondrecognition function, a larger value range of the detected mechanicalquantity 3 leads to the recognition of a kickback event than with thefirst recognition function.

The second recognition function is therefore, for example, more suitablefor less experienced users of the power tool, since the secondrecognition function recognizes a wider range of kickbacks—especiallyalso weaker kickbacks. The first recognition function, on the otherhand, is, for example, more suitable for trained or very experiencedusers of the power tool 10 who can handle weaker kickbacks even withoutthe assistance of the power tool 10. Since the first recognitionfunction does not detect or ignores weaker kickbacks, the use of thefirst recognition function can prevent, for a trained or veryexperienced user, the kickback recognition from causing unnecessary andinterfering interruptions of the machining process.

As mentioned above, the mechanical quantity 3 is preferably detected asa vector quantity. In this case, the kickback event can in particular bedetected based on a direction and/or a change in direction of the vectorquantity. For example, the control device 4 is adapted to determinewhether the direction of a mechanical quantity 3, detected as a vectorquantity, lies within or outside a specific directional range and todecide based on this determination whether or not the kickback event ispresent.

With reference to FIG. 2, a recognition of the kickback event based on avector quantity is explained below.

FIG. 2 shows a diagram with different directional ranges 14, 15 and thedetected mechanical quantity 3.

The diagram is divided into four quadrants. Each quadrant covers 90degrees. The reference sign 19 indicates the zero degree line. The anglecoordinates or degrees mentioned below are to be understood in themathematically positive direction of rotation (counter-clockwise).Expediently, the zero degree line runs parallel to the contact surface 9and/or to the feed direction 12.

The directional ranges 14, 15 are exemplarily two-dimensionaldirectional ranges. The directional ranges 14, 15 can also be calledangular ranges. Expediently, the directional ranges 14, 15 lie in aplane. The plane is expediently aligned parallel to the plane of thetool 1 or perpendicular to the axial direction of the output shaft 8.

The two directional ranges 14, 15 differ from each other. As an example,the first directional range 14 is within the second directional range15. The first directional range is expediently smaller than the seconddirectional range 15.

Expediently, the first directional range 14 belongs to the firstrecognition function. The first recognition function includes inparticular a comparison of a direction of the mechanical vector quantitywith the first directional range 14. The second directional range 15expediently belongs to the second recognition function. The secondrecognition function includes in particular a comparison of thedirection of the mechanical vector quantity with the second directionalrange 15.

The control device 4 is expediently adapted to provide the firstdirectional range 14 and the second directional range 15. For example,both directional ranges are stored in a memory in the control device 4.Alternatively or in addition to this, the control device 4 can also beadapted to generate the directional ranges 14, 15 itself.

The first directional range 14 represents a directional range in whichthe mechanical vector quantity is located if, with very highprobability, a kickback is present or is imminent. As an example, thefirst directional range 14 is located in the two upper quadrants, i.e.within a range between 0 degrees and 180 degrees. In the example shown,the first directional range 14 extends from 5 degrees to 100 degrees. Ifthe control device 4 uses the first recognition function, the kickbackevent is recognized if the mechanical vector quantity 3 lies within thefirst directional range 14.

The second directional range 15 is larger than the first directionalrange 14. As an example, the second directional range 15 is located inthe first, second and fourth quadrants, i.e. within a range between 270degrees (or −90 degrees) and 180 degrees. In the example shown, thesecond directional range 15 extends from 340 degrees (or −20 degrees) to120 degrees. The second directional range 15 covers not only directionsin which a kickback can be inferred with a very high probability, butalso directions in which a kickback is still possible but less likelythan in the first directional range 14. In particular, the seconddirectional range 15 also includes directions in which the cause or aninitial indicator of the kickback is already given, but the power tool10 or the workpiece 11 have not yet been significantly accelerated orhave not yet exerted any recoil. Expediently, the control device may beadapted to detect, when using the second directional range 15, thekickback event 50 to 100 ms before an acceleration of the power tool 10relative to workpiece 11 would take place (without a recognition and aresponse to the kickback). The acceleration is, for example, anacceleration with one component upwards or one component in a 90 degreedirection in the diagram shown.

Expediently, the control device is adapted to recognize that there is nokickback event if the mechanical quantity 3 is outside the firstdirectional range 14 or outside the second directional range 15.

As an alternative or in addition to the recognition of the kickbackevent based on the direction of the detected mechanical vector quantitydescribed above, it is also possible to perform the recognition of thekickback event based on a change in direction of the mechanical vectorquantity.

Accordingly, the first and second recognition functions may include acomparison of a change of direction, in particular an angular velocityand/or angle of change, of the mechanical vector quantity with arespective directional change threshold.

If a kickback is imminent, the mechanical vector quantity rotates in thedirection towards the first directional range 14 The recognitionfunctions can accordingly take into account a detected rotation of themechanical vector quantity when recognizing the kickback event. Forexample, the control device 4 is adapted to compare the angular velocityof the mechanical vector quantity with a velocity threshold and torecognize the kickback event if the velocity threshold is exceeded. Forthe first recognition function, a different, in particular a highervelocity threshold can be used than for the second recognition function.

Furthermore, the control device 4 may be adapted to determine the angleof change by which the mechanical vector quantity 3 has changed, inparticular within a specific time window, and to compare this angle ofchange with an angle threshold in order to recognize the kickback event.For the first recognition function, a different, in particular a largerangular threshold can be used than for the second recognition function.

In addition, the recognition functions can take into account the timeduration that the mechanical vector quantity 3 is within a specificdirectional range 14, 15. For example, the control device 4 may beadapted to recognize the kickback event only if the mechanical vectorquantity is within a specific directional range 14, 15 for longer than aspecific time threshold. For the first recognition function, adifferent, in particular a larger time threshold value can be used thanfor the second recognition function.

The above explained specific angle figures of the directional ranges 14,15 are to be understood purely as examples. Actual angles may varydepending on the type and construction of the power tool 10. The actualangles of the directional ranges 14, 15 can be determined bycalibration. Calibration can be carried out, for example, during thedevelopment or manufacture of the power tool and/or by the user.

Expediently, the control device 4 is adapted to calibrate one or moredirectional ranges 14, 15. For example, the calibration can be initiatedvia the user interface 5. The control device 4 can then drive the tool 1via the drive device 7 and, while doing so, detect the mechanical vectorquantity 3 via the sensor device 2. Based on the detected mechanicalvector quantity 3, the control device 4 can then create a directionalrange and/or one or more thresholds and store them in a memory of thecontrol device 2.

In the following, it is explained by way of example how the recognitionfunction to be used can be determined.

Basically, the control device 4 determines the recognition function tobe used based on the function determination information. The functiondetermination information is either provided externally to the controldevice 4 or is created in the control device 4.

For example, the function determination information can be entered viathe user input device 5. As an example, a user can choose, via the userinput device 5, between two different safety profiles—e.g. a beginnerprofile and a professional profile. According to the user's input orchoice, the control device 4 then uses either the first recognitionfunction or the second recognition function.

Further, the control device 4 can receive the function determinationinformation via the communication interface 35. For example, the controldevice 4 can communicate via the communication interface with anexternal device 3, such as a server or a mobile device, and receive thefunction determination information from this external device 3.According to the received function determination information, thecontroller then uses either the first recognition function or the secondrecognition function.

As an example, the function determination information can also beprovided in the control device 4. For example, the control device 4 isadapted to identify a user by means of the user identification device 36and provide the function determination information according to theidentification. For example, an assignment between different users andthe recognition functions can be stored in the control device 4, so thatwhen the user is identified, the assigned recognition function can beselected and used.

As an example, the control device is further adapted to provide thefunction determination information based on an operating informationand/or environmental information detected by the sensor device 2, inparticular the second sensor unit 34. For example, the control device 4can use the sensor device 2 to detect a state of the tool, workpieceand/or environment and determine the recognition function to be usedbased on this.

It is also possible that the control device 4 cooperates with theexternal device 38, in particular the server or mobile device, via thecommunication interface 35 to identify the user and/or to provide thefunction determination information. In this case, the power tool 10 andthe external device 38 can together form a system. For example, thepower tool 10 is adapted to transmit operating information and/orenvironmental information and/or user identification information to theexternal device 38. The external device 38 is expediently adapted toprovide and transmit the function determination information to the powertool based on the operating information and/or environmental informationand/or the user identification information.

For example, as the user identification information, informationrecorded with the user identification device, such as biometricinformation, can be transmitted to the external device 38. In theexternal device 38, a user identity and/or function determinationinformation can then be determined, for example by referring to adatabase stored there. The user identity and/or function determinationinformation can then be transmitted via the communication interface 35to the control device 4 for further use.

In the above discussion, two recognition functions are always mentioned.Of course, the control device 4 can also have more than two differentrecognition functions available for recognizing the kickback event.

For example, the recognition functions available to the control device 4may be stored in a memory of control device 4. According to the functiondetermination information, the control device 4 then selects arecognition function and uses it to detect a kickback event. In thiscase, the function determination information can include, for example,the information which recognition function is to be used.

Alternatively, or in addition thereto, the control device 4 may create,by itself, a recognition function to be used, the creation beingexpediently based on the function determination information. Forexample, the function determination information may specify a parameterto be used for the recognition function, such as a threshold, and/or amathematical operator to be used.

Below, exemplary possibilities are explained how the mechanical quantity3 can be detected as a vector quantity.

The sensor device 2 is expediently adapted to detect the mechanicalvector quantity 3 as an at least two-dimensional vector. For thispurpose, the sensor device 2 is adapted to measure the mechanicalquantity underlying the mechanical vector quantity 3 in at least twodifferent spatial directions. The two spatial directions are, forexample, a spatial direction parallel to the feed direction 12 and aspatial direction perpendicular to the feed direction 12. Expediently,both spatial directions are perpendicular to the axial direction of theoutput shaft 8. For example, the sensor device 2 has at least two sensorelements 25, 26. Expediently, each of the sensor elements 25, 26 servesto measure the underlying mechanical quantity—i.e. a force, anacceleration, a velocity, a deflection, a deformation and/or amechanical stress—in a different spatial direction.

The mechanical vector quantity 3 is in particular a force vector, anacceleration vector, a velocity vector, a deflection vector, adeformation vector and/or a mechanical stress vector or stress tensor.Accordingly, the sensor device 2 can be adapted to measure, in at leasttwo spatial directions, a force, an acceleration, a velocity, adeflection, a deformation and/or a mechanical stress.

The sensor device 2 may in particular comprise a radial measuringbearing 28, with which, for example, the output shaft 8 is mounted. Theradial measuring bearing 28 can be adapted to measure, by means of forcesensors or stress sensors, for example piezoresistive sensors, the forcebetween the output shaft 8 and the measuring bearing 28 as themechanical vector quantity 3.

Alternatively or in addition thereto, the sensor device 2 may comprisedistance sensors spaced from the output shaft 8 and adapted to detectthe deflection of the output shaft 8 as the mechanical vector quantity3.

Further, the sensor device 2 may include stress sensors, such as straingauges (SG), in particular attached to the support structure 21.

Basically, the sensor device 2 can be set up to measure the mechanicalvector quantity 3 at a part within the force flow emanating from thetool 1. The force flow runs exemplarily from the tool 1 via the outputshaft 8, a bearing device 27, the support structure 21, the housing 6and the contact surface 9 to the workpiece 11. In particular, the sensordevice 2 is adapted to measure the mechanical vector quantity 3 betweentwo parts lying one behind the other in the force flow.

FIG. 3 shows a sectional view of the power tool 20. The aboveexplanations related to the power tool 10 also apply to the power tool20.

As shown in FIG. 3, the power tool 20 comprises a bearing device 27,which is provided on the support structure 21 and mounts the outputshaft 8 relative to the support structure 21. The bearing device 27expediently comprises one or more bearings 31, 32, in particular radialand/or radiaxial bearings, preferably ball bearings.

Expediently, at least one bearing 31, 32 of the bearing device 27 isdesigned as a measuring bearing 28, in particular as a radial measuringbearing, and can therefore serve as the sensor device 2. The measuringbearing 28 is preferably adapted to measure a force present between theoutput shaft 8 and the support structure 21 in at least two differentspatial directions. For example, the measuring bearing 28 has aplurality of sensor elements, for example piezoresistive sensorelements, in particular piezoresistive thin-film sensor elements, whichare expediently arranged in a circumferential direction around theoutput shaft 8. In particular, the sensor elements are arranged on anouter bearing component of the measuring bearing 28—i.e. a bearingcomponent that is stationary relative to the support structure 21 or abearing component that does not rotate with the output shaft 8, such asan outer ring. As an example, eight sensor elements are provided, whichare offset by 45 degrees to each other.

FIG. 4 shows the output shaft 8 together with two bearings 31, 32 of thebearing device 27. Exemplarily, the first bearing 31 is located in thearea of a distal end of the output shaft 8, the distal end beingassigned to the tool 1, and the second bearing 32 is located in the areaof a distal end of the output shaft 8, the distal end facing away fromthe tool 1.

Expediently, one or both bearings 1, 2 is/are designed as the measuringbearing 28 explained above.

As an alternative or in addition to the embodiment explained above,where the sensor device 2 is internally integrated in one or morebearings 31, 32, the sensor device 2 may also be located between one ormore bearings 31, 32 and the support structure 21.

FIG. 5 shows a power tool 30 according to a sixth embodiment. The powertool 30 is here exemplarily designed as a stationary saw, in particularas a circular table saw. The power tool 30 expediently includes thefeatures already discussed above in connection with the power tool 10and/or the power tool 20.

As an example, the tool 1 here rotates counterclockwise. Expediently,the workpiece 11 is pushed into the tool 1, which is designed as a sawblade, so that the saw teeth saw into the workpiece 11 from top tobottom. FIG. 8 shows a corresponding feed direction 12. The directionalranges 14, 15 are adapted accordingly for the power tool 60. Forexample, the directional ranges 14, 15 shown in FIG. 2 can bepoint-mirrored around the center of the diagram.

In the following, different possibilities are discussed how to react toa detected kickback event. Expediently, each of these possibilities ispresent for each of the power tools discussed above.

Preferably, the control device 4 may be adapted to perform a specificcontrol of the drive device 7 in response to the detected kickbackevent, for example to cause that the tool 1 is no longer being drivenand/or is braked, in particular braked completely. In particular,braking can be carried out with the same electric motor that isotherwise used to drive the tool 1. Alternatively or in additionthereto, the drive device 7 may include a braking means and the controldevice 4 may be adapted to control the braking means in response to thedetected kickback event so that the tool 1 is braked.

Furthermore, the power tool 10, 30 may include a positioning device 29adapted to position the tool 1 either in an operating position or in asafety position. The control device 4 can be adapted to control thepositioning device 29 in response to the detected kickback event so thatthe tool 1 is positioned in the safety position. The positioning device29 is adapted, for example, to move and/or swivel the tool 1 between theoperating position and the safety position. Expediently, the tool 1 ispositioned, in the safety position, further into the housing 6 than inthe operating position.

FIG. 6 shows a flow chart of a method for recognizing a kickback eventof a power tool with a rotatable tool designed as a saw blade or amilling cutter. The method comprises the steps of: detecting, S1, amechanical quantity 3, wherein the mechanical quantity 3 comprises aforce, an acceleration, a velocity, a deflection, a deformation and/or amechanical stress, and the mechanical quantity 3 depends on a forceemanating from the tool 1, determining, S2, based on a functiondetermination information, a recognition function to be used from afirst recognition function and a second recognition function differentfrom the first recognition function, and recognizing, S3, using thedetermined recognition function, the kickback event based on thedetected mechanical quantity 3.

Expediently, one of the power tools 10; 20; 30 described above is usedfor carrying out the method.

Preferably, the method has a further step in which one of the reactionsdiscussed above is executed in response to the detected kickback event.

1. A power tool with a rotatable tool designed as a saw blade or amilling cutter, comprising: a sensor device for detecting a mechanicalquantity, the mechanical quantity comprising a force, an acceleration, avelocity, a deflection, a deformation and/or a mechanical stress, andthe mechanical quantity being dependent on a force emanating from thetool, and a control device communicatively coupled to the sensor device,which control device is adapted to recognize a kickback event based onthe detected mechanical quantity, wherein the control device is adaptedto selectively determine, based on a function determination information,a first recognition function or a second recognition function differentfrom the first recognition function, and to perform the recognition ofthe kickback event based on the detected mechanical quantity using thedetermined recognition function.
 2. The power tool according to claim 1,wherein the power tool has a communication interface for communicationwith an external device, wherein the control device is adapted toreceive the function determination information via the communicationinterface.
 3. The power tool according to claim 1, wherein the powertool has a user identification device, wherein the control device isadapted to provide the function determination information based on anidentification of a user of the power tool made by means of the useridentification device.
 4. A system comprising the power tool accordingto claim 1 and an external device, wherein the power tool is adapted totransmit operating information and/or environmental information and/oruser identification information to the external device and the externaldevice is adapted to provide the function determination informationbased on the operating information and/or environmental informationand/or the user identification information and to transmit the functiondetermination information to the power tool.
 5. The system according toclaim 4, wherein the external device is a server.
 6. The power toolaccording to claim 1, wherein the two recognition functions differ intheir sensitivity.
 7. The power tool according to claim 1, wherein thefirst recognition function comprises a comparison of the detectedmechanical quantity with a first threshold and the second recognitionfunction comprises a comparison of the detected mechanical quantity witha second threshold different from the first threshold.
 8. The power toolaccording to claim 1, wherein the control device is adapted to perform acalibration of at least one recognition function.
 9. The power toolaccording to claim 1, wherein the power tool comprises a drive devicefor driving the tool and the control device is adapted to control thedrive device in response to the detected kickback event in order tochange the driving of the tool.
 10. The power tool according to claim 9,wherein the control device is adapted to control the drive device inresponse to the detected kickback event in order to brake the tool. 11.A method for recognizing a kickback event of a power tool with arotatable tool designed as a saw blade or a milling cutter, comprisingthe steps: detecting a mechanical quantity, wherein the mechanicalquantity comprises a force, an acceleration, a velocity, a deflection, adeformation and/or a mechanical stress and the mechanical quantitydepends on a force emanating from the tool, determining, based onfunction determination information, a recognition function to be usedfrom a first recognition function and a second recognition functiondifferent from the first recognition function, and recognizing, usingthe determined recognition function, the kickback event based on thedetected mechanical quantity.